The present invention generally relates to a coupling system or mechanism for an optical apparatus including a main body and an optical assembly detachably attachable to or mountable on the main body such that a driven member in the optical assembly is connected with a driving member in the main body. The optical assembly may be, for example, a photographic camera, a motion picture camera, a TV camera, a still or motion picture projector, a photographic printer or enlarger, or the like, wherein an interchangeable lens assembly is detachably attached to or mounted on a main body and a driving mechanism in the main body is connected with a driven member in the lens assembly for the driving of one or more optical elements therein, i.e., for focusing, zooming or the like.